A woman's work is never done. Though you might not know it to look at her paycheck.

Did you know that, according to the AFL-CIO, the average 25-year-old woman who works full-time, year-round until she retires at age 65 (if that's when she's able to retire) will earn $523,000 less than the average working man?

At the current rate of change, working women will not achieve equal pay until after the year 2050. That's almost 100 years after President Kennedy signed the Equal Pay Act into law, prohibiting discrimination based on sex resulting in unequal pay for equal work.

On average, women make 78 percent of men's wages, according to a 2003 study by the U.S. Department of Labor. This is, however, a marked improvement over 25 years ago -- in 1979, women made 62 percent of what men earned.

It varies by race

The pay gap differs by race, with the earnings of white women being just 78 percent of those of white men; black women making 91 percent as much as their male counterparts; and Hispanic women earning 88 percent of what Hispanic men earn. The Rutgers School of Management Relations says this is primarily because white men still earn the most among all groups of workers.

It's wider among professionals

Even though women earn less than do men at all education levels, women are gaining ground. Earnings for women with a college degree have risen by one-third since 1979, versus only 19 percent for men.

Interestingly, the wage gap is largest among the most highly educated groups.A researcher exploring the pay and promotion gap among statisticians attributed this to women not wanting to put themselves forward as candidates for competition. She found that while most women did not apply for higher jobs because they believed they needed more time and preparation, ironically, those who did apply actually had more success than their male counterparts.

While causes of the gender pay gap are complex and include work/family choices, data on women's dramatically lower recognition in domains where their talents and achievements are equal to men's imply there is a tendency to undervalue a woman's work and contributions.

Occupation matters

The pay gap appears in all occupations, including those with severe shortages where salaries should be the most competitive to attract top candidates. Consider physicians, with numbers declining due to high insurance costs and the number of years in training. Females doctors only earn 58 percent of their male counterparts' salaries. Even in predominantly female fields like nursing and teaching, women still earn less than men: female nurses earn 91 percent and female teachers earn 87 percent of what their male counterparts do.

Jobs with the smallest gender pay gaps include legal assistants, where women earn 90 percent of what men do, as well as male-dominated occupations like engineering, where women earn 92 percent as much as men, and police and detective work, where women earn almost 80 percent as much as men do.

According to Labor Department figures, women who choose nontraditional careers such as dentists (just 20 percent are women) or airline pilots or navigators (less than 4 percent are female), can expect to have lifetime earnings that are 150 percent higher than those of women who choose traditional careers.

Pay vs. satisfaction

Despite the pay gap, according to several studies, women are actually more satisfied at work!

CareerBuilder.com's recent "Pulse of the Worker" survey found that despite receiving lower raises, fewer bonuses and having lower expectations for being promoted, women were more likely than men to report that, overall, they are happy with their jobs.